1. Field of the Invention
This invention relates, in general, to power line carrier communication systems and, more specifically, to component arrangements for carrier communications over secondary distribution lines.
2. Description of the Prior Art
Carrier communication systems have been used on high voltage power transmission lines for a number of years. Recently, much interest has developed concerning the use of carrier communications along the primary and secondary power distribution lines. The recent interest in such systems has been prompted by the desire to obtain more knowledge about the electrical power being used at the customer location and as a means for controlling certain parameters of that power usage.
Tests have indicated that the optimum frequency bands for carrier transmission along the primary and secondary distribution lines are different. Thus, it has been found desirable to translate the carrier frequencies between the primary and secondary distribution lines. In addition to translating carrier frequencies, it has been found that, due to the high attenuation of distribution transformers to carrier communication signals, a repeater connected to the primary and secondary distribution lines enhances the effectiveness of the carrier communication system. Thus, systems have been disclosed which use a coupler or repeater-translator around each distribution transformer in the portion of the electrical power system on which communications is desired.
While such repeaters provide reliable carrier communication systems, the economy of such systems sometimes suffers due to inefficient use of the repeaters. Each repeater is capable of repeating or translating carrier communication signals to and from a number of customer load locations. A conventional repeater is able to serve up to sixteen customer loads. However, many secondary distribution lines do not serve the number of customer loads which can be served by the repeater. Actually, some secondary distribution lines serve only one customer when this customer requires a large amount of power. Therefore, with conventional secondary distribution power line arrangements, many of the distribution transformer repeaters can not be fully used to their capacity.
Secondary distribution power lines are arranged in many different patterns, usually with one distribution transformer connected to each separate or independent secondary distribution line. Although separate secondary distribution lines may be connected to the same supporting structure for stability and proper guying requirements, the separate distribution lines are not electrically connected together for power transmission. Therefore, according to conventional arrangements, a repeater is required to be connected around each distribution transformer associated with each separate secondary distribution line, although the associated secondary distribution line may be serving less than the total number of customer loads which the repeater is capable of serving.
In other secondary distribution line arrangements, the distribution lines may run parallel to each other for a considerable distance. However, such secondary distribution lines are connected through separate distribution transformers to the primary distribution line. This type of arrangement also does not make full use of the repeaters around the distribution transformers when less than the full capacity of loads is being served by a repeater. Therefore, it is desirable, and it is an object of this invention, to provide a power line carrier communication system which provides economical use of the repeaters located at the distribution transformers.